This invention pertains to fluid bed, catalytic oxychlorination of ethylene to produce 1,2 dichloroethane, commonly called ethylene dichloride (EDC), and relates specifically to improved copper chloride catalysts and their use in an ethylene oxychlorination reaction.
The production of chlorinated hydrocarbons by oxychlorination is known to the art. For example, a well known process for oxychlorination of ethylene to produce EDC, practiced in many commercial installations throughout the world, involves the vapor phase reaction, over a fluidized catalyst bed, of a mixture of ethylene, hydrogen chloride (HCl) and oxygen or an oxygen containing gas (e.g., air) in the manner and under the conditions described in U.S. Pat. No. 3,488,398 granted to Harpring et al.
A typical catalyst used in fluid bed oxychlorination reactions comprises about 4% to 17% by weight of a copper compound. Typically, the copper compound is cupric chloride, as the active catalytic ingredient, deposited on particles of a fluidizable support, such as silica, kieselguhr, clay, fuller's earth, or alumina. The support should be readily fluidizable without excessive catalyst loss from the reaction zone, and have proper bulk density, resistance to attrition and particle size and distribution to be useful in the process. In prior art oxychlorintion processes most closely aligned to the present invention, an alumina support is employed which may be gamma alumina, alpha alumina, the so-called microgel aluminas or other forms of "activated" alumina. The standard, fluid bed alumina-based oxychlorination catalysts can be improved upon in significant respects.
First, it is desirable for the oxychlorination catalyst to effect the highest possible yield of EDC based on ethylene (i.e., for the ethylene to be more completely converted to EDC, with less ethylene being reacted to carbon oxides or higher chlorinated materials). In the high volume business of manufacturing EDC, small increases in the efficiency of ethylene conversion to EDC are very valuable. For example, in a one billion pound per year EDC oxychlorination plant, an ethylene efficiency increase of only 1% can result in a savings of from about 0.4 to about 1.0 million dollars annually. Further, increased ethylene efficiency reduces the potential of release of hydrocarbons and chlorinated hydrocarbons to the environment.
Second, it is becoming much more desirable for economic and environmental reasons, for the oxychlorination catalyst to also effect a high conversion of the hydrogen chloride (HCl) used in the reaction. Problems can arise when a higher than theoretical molar ratio of HCl to ethylene is used in an attempt to achieve higher ethylene conversions to EDC. Unconverted HCl must be neutralized using, for example, a caustic solution, and the resulting salt must be disposed. Also, higher levels of HCl in the process can lead to higher HCl "break through" downstream of the reactor which can cause corrosion problems. Hence, a modern oxychlorination process will attempt to operate at an HCl to ethylene molar ratio as close to the theoretical level of two-to-one (2:1) as possible in conjunction with high HCl conversion. In such an operation, a combination of high HCL conversion and high ethylene efficiency is most desirable.
Lastly, typical cupric chloride on alumina, fluid bed catalysts exhibit a strong tendency to develop "stickiness" during the oxychlorination reaction at HCl to ethylene molar feed ratios of about 1.9 to 2.0. Catalyst stickiness, which is basically agglomeration of catalyst particles, is a critical barrier to achieving optimum ethylene and HCl feedstock efficiencies in a fluid bed oxychlorination process. High ethylene efficiency from an oxychlorination catalyst requires operation with an HCl/ethylene molar feed ratio approaching the stoichiometric value of 2.0. However, as the HCl/ethylene feed ratio is increased above about 1.9 in a commercial process, standard fluid bed oxychlorination catalysts become progressively more sticky. With increased catalyst stickiness, heat transfer characteristics of the fluid bed worsen, hot spots develop within the catalyst bed, feedstock conversions and yields decline, and, in extreme cases, the bed actually collapses and slumps causing vapor passages through the bed. Therefore, a high performance oxychlorination catalyst requires operation with HCl/ethylene feed ratios approaching 2.0, excellent fluidization, and high conversions, yields, and efficiencies. This problem of catalyst stickiness and a device and means for its partial control are described in U.S. Pat. No. 4,226,798 issued to Cowfer et al. A method of controlling stickiness in standard oxychlorination catalysts is also described in U.S. Pat. No. 4,339,620 also issued to Cowfer et al. Although these devices and methods are helpful, it is more practical and efficient to employ an oxychlorination catalyst which does not develop stickiness during the reaction.
By way of further background, it has been proposed in the prior art to conduct oxychlorination reactions using a fluid bed catalyst in which the catalyst contains not only copper chloride but other metal compounds such as chlorides and oxides of alkali metals, alkaline earth metals, transition metals, and/or rare earth metals. For example, U.S. Pat. No. 3,427,359 describes a catalyst composition useful for fluid-bed oxychlorination of hydrocarbons consisting of copper chloride, an alkali metal chloride and/or a rare earth metal chloride supported on an alpha alumina having a surface area no greater than 10 m.sup.2 /g. Likewise, U.S. Pat. Nos. 3,657,367; 3,914,328; 3,992,463; 4,069,170; 4,124,534 and 4,284,833 and Canadian Pat. No. 701,913 all teach the use of metal chlorides deposited with copper chloride on low surface area (alumina) supports. However, these low surface area support catalysts are not useful in the fluid bed ethylene oxychlorination process of the present invention because the ethylene efficiency is very low.
There are also patents which disclose the use of alkali metals, alkaline earth metals, and/or rare earth metals along with copper chloride on high surface area supports. For example, U.S. Pat. Nos. 3,468,968; 3,642,921; and 4,123,389 all broadly disclose the use of a catalyst of copper chloride and alkali metals such as KCl, and/or rare earth metals such as cerium, praeseodymium, neodymium, and lanthamum. Whereas these catalysts are closer in composition to those of the present invention, optimization in composition and improvements in performance can still be obtained. All of these references are deficient in that none teach or suggest the optimization of the ratio of the types of metals used to each other in affecting catalyst performance.
Lastly, other patents in the prior art do teach or suggest that better catalysts are obtained if the added metals are employed in a certain weight or molar ratio of added metal(s) to the copper present. For example, U.S. Pat. Nos. 3,205,280; 3,308,189; 3,308,197; 3,527,819; 3,769,362; 3,862,996; 4,046,821; 4,123,467; 4,206,180; 4,239,527; 4,329,527; 4,451,683 and 4,460,699 all broadly disclose that a certain weight or mole ratio of added metal to copper improves the catalyst.
From the above, it is readily seen that much effort has been put into developing "optimum" catalysts for oxychlorination reactions. Of all the above-referenced patents, it is worthwhile to note those patents most closely aligned with the catalyst and process of the present invention. U.S. Pat. No. 3,205,280 discloses a catalyst composition of an Al.sub.2 O.sub.3 support (calcined at 900.degree. C. which substantially lowers its surface area) having thereon an alkali metal such as potassium chloride, an alkaline earth metal, a transition metal such as copper, and/or a rare earth metal such as didymium. The atomic ratio of alkali or alkaline earth metal to transition or rare earth metal is at least one-to-one to no more than seven-to-one. Preferably, the patent teaches an atomic ratio of alkali metal to transition metal to rare earth metal of 4:1:1. A catalyst of KCl, DiCl.sub.2, and CuCl.sub.2 on alpha-Al.sub.2 O.sub.3 is shown in Example IV.
U.S. Pat. No. 3,308,197 broadly teaches a catalyst composition of aluminum oxide containing Group Ia and/or IIa metals such as potassium chloride and a Group IIIb metal such as ceric oxide, wherein the ratio of metal atoms from Groups Ia and IIa to Group IIIb is from 0.01 to 1.5 : 1. A catalyst of CeO.sub.2 and KOH on Vycor Raschig rings is disclosed in Example 6.
U.S. Pat. No. 3,527,819 broadly teaches a process for preparing tri-and tetrachloroethylene using a catalyst composition of copper chloride, potassium chloride, and neodymium chloride on a high surface area silica gel support. The atomic ratio of potassium to copper in the catalyst is 0.6 to 1 : 3 to 1, and the atomic ratio of neodymium to copper is at least 0.4 to 1. The patent's teaching is specific to neodymium chloride. However, comparative catalysts containing up to 2.5% by weight of rare earth metals are shown in Table 1.
U.S. Pat. No. 3,862,996 broadly teaches a process for preparing ethylene from ethane using a catalyst composition of an alumina support containing copper halide and a rare earth metal halide, and optionally an alkali metal halide such as KCl or LiCl. The weight ratio of rare earth metal halide to copper halide in the catalyst is greater than one-to-one. A catalyst of CuCl.sub.2, rare earth metal halide (cerium halide and didymium halide) and LiCl on an alumina support is shown in the Examples.
U.S. Pat. No. 4,046,821 broadly teaches a catalyst composition of a low surface area support containing a copper (non-halide) compound such as CuCO.sub.3, a rare earth metal compound, and optionally an alkali metal compound. The atomic ratio of rare earth metal to copper in the catalyst is 4 to 0.1 to 1. Catalysts of CuCO.sub.3, CeO.sub.2 and KCl on a low surface area alumina are shown.
Lastly, U.S. Pat. No. 4,451,683 broadly teaches a catalyst composition of a copper compound such as CuCl.sub.2, an alkali metal such as KCl, and a rare earth metal such as CeCl.sub.3 on a high surface area magnesium oxide - aluminum oxide support. The number of alkali metal ions in the catalyst is less than 100 per 100 ions of copper. A catalyst of CuCl.sub.2, KCl, and CeCl.sub.3 on a high surface area MgO,Al.sub.2 O.sub.3,Na.sub.2 O support is shown in Table 3.
The deficiency in the above patents is that none of these patents teach or disclose the effect of the ratio of rare earth metal to alkali metal on catalyst stickiness and performance.
As a final prior art reference, U.S. Pat. No. 4,446,249, issued to J. Eden, one of the present inventors, discloses a method of obtaining an improved oxychlorination catalyst of cupric chloride on a gamma-alumina support, modified with one or more of an alkali metal, an alkaline earth metal, and/or a rare earth metal wherein the critical feature of the patent consists of "fixing" the modifying metal(s) to the support by a calcination step prior to deposition of the cupric chloride. The pre-calcination of the modifying metal(s) to the support before adding the copper makes the catalyst composition less prone to stickiness during use. The catalysts of the present invention are distinguished over this prior art in that, in the present invention, a fluidizable (non-sticky), high ethylene efficiency, high HCl conversion catalyst is obtained without the need of calcining the alkali metal and rare earth metal to the support before depositing the cupric chloride.